The invention relates to the operation of a furnace for the treatment of objects (substrates) such as wafers with a reactive gas. Such a reactive gas can comprise hydrogen or another gas that, if it comes into contact with air, can form an explosive mixture.
In the prior art this problem is avoided by providing an additional tube surrounding the process tube hermetically and purging the gap between the process tube and the outer tube with an inert gas. However, in case an event results in heavy damage of the process tube, and consequently, in escape of reactive gas from the process tube, it is likely that the same event results also in heavy damage of the outer tube because both tubes are closely connected together and both tubes are made of refractory materials like quartz or silicon carbide which are susceptible to breakage upon mechanical impact. Such an event can be an earthquake which are regular phenomena is some of the worlds most important semiconductor manufacturing areas. Also it is possible that, because of the close connection of the tubes, breakage of one tube induces breakage of the other tube.
It is an object of the invention to provide a method for the treatment of an object in a furnace, wherein it is possible to use a high concentration of reactive gas without the risk of an explosion.
It is a further object of the present invention to provide a furnace in combination with conduits (system) with which the treatment of a substrate with a reactive gas in a comparatively high concentration is possible.
Is a further object of the present invention to carry out such a treatment at a comparatively high temperature.
According to a further object of the present invention it is intended, after the treatment at a comparatively high temperature, to comparatively quickly and uniformly realize cooling of the process space and thus of the substrate.
According to an aspect of the invention, a method is provided for purging a furnace comprising a closable processing tube defining in its interior a closable processing space, a purging gas being flowed along the outer surface of the processing tube separated from the processing gas flow inside the processing tube, wherein said processing gas flow comprises a gas being reactive with air at elevated temperature and said purging gas comprises at least 90 vol. % of an inert gas.
According to a further aspect of the invention, the purging gas comprises at least 99% by volume of an inert gas. Nitrogen can be used as the inert gas. Furthermore the purging gas can comprise at least 100 ppm by volume of an oxidizing gas and preferably at least 0.1% by volume of an oxidizing gas. According to a preferred embodiment of the invention, the reactive gas comprises at least 6% by volume of hydrogen.
The oxidizing gas can comprise oxide, H2O, CO2 or N2O alone or in any combination. Preferably oxygen or air (compressed) is used.
The pressure in the furnace or other treatment room is preferably atmospheric. According to a further aspect of the invention, the purging gas is not only used for purging the furnace as well as the space around it, but the purging gas also acts as a cooling medium.
Optimal safety is achieved if the treatment space is also purged, this purging preferably taking place after the treatment has finished, but before the treatment room is brought into contact with the environment.
If the purging gas is used for cooling, according to a special embodiment of the invention, the direction of movement of this gas is periodically reversed so that an even cooling occurs from the inlet to the outlet.
According to a further aspect, the invention relates to a method for treating a substrate in a furnace at elevated temperature with a processing gas, said processing gas being reactive with air at processing temperature of said substrate, wherein after said substrate is introduced in said furnace, the processing chamber thereof is purged with an inert gas before reactive processing gas is introduced in said processing chamber.
Moreover, the invention relates to a furnace assembly comprising a furnace having a processing chamber surrounded by heating means, said processing chamber having a removable closure, at least a gas inflow and gas outflow opening, said gas inflow opening being connected to at least two supply conduits each comprising a controller controlled valve and connected to a source of reactive and inert gas respectively, a controller for controlling said valves such that only after placing said closure in the closing position in said processing chamber the valve in the supply conduit for reactive gas can be opened and said closure can only be removed from said closing position after said valve in supply conduits for reactive gas has been closed.
Preferably the space through which the purge gas is conducted is defined by the heating element and/or the isolation thereof.
Moreover, safety measures are present. These are implemented such that the continuous purging during a certain period of time is guaranteed before the reactive gas is brought into the treatment space (while it is closed) or before the treatment space is brought into contact with the environment. Likewise (constant) checks are made on the purging gasses for the presence of oxygen to detect any leaks in the system.
According to a further aspect of the invention there are various valves for the supply of process gas and inert respectively purging gas, implemented such that when the energy supply fails, the supply of the inert/purging gas is still guaranteed.
The invention will be explained below with reference to two embodiments, schematically shown in the attached drawing, wherein the advantages and particular qualities of the invention are elucidated, and wherein: